Gas generating compositions and apparatus

ABSTRACT

A gas generator for inflating a bag comprising a deflagration composition yielding a gas comprising principally carbon dioxide and water vapor comprises a substantially homogeneous mixture of citric acid powder in the range of from about 23 to 37 percent by weight and an oxidizer powder selected from the group consisting of potassium chlorate, potassium perchlorate sodium chlorate, and sodium perchlorate. This composition is used adjacent a coolant powder comprising up to about 40 percent by weight of potassium chlorate and an endothermic decomposition coolant having a thermal decomposition product selected from the class consisting of carbon dioxide and water.

United States Patent [l ll 3,880,595

Timmerman Apr. 29, 1975 [54] GAS GENERATING COMPOSITIONS AND 3.558.2851/197! Cicconc et al 23/281 R T S 3,690,97l 9/1972 Gunderloy et al.l49/76 X 3,733,]80 5/1973 Heineck et al 23/281 Inventor: HubertTimmerman. 1809 3.77335: 11/1973 Catanzarite 23/28] x Faymont Ave.,Manhattan Beach, 3,837,942 9/1974 Catanzarite 102/39 X Calif. 90266Primary Examiner-Joseph Scovronek (22} Filed 1973 AssistantExaminerBarry I. Hollander l PP 390435 Attorney. Agent, or FirmChristie,Parker & Hale Related U.S. Application Data [62] Division of Ser. No.26l,()4l. June 8, 1972. Pat, No. 1571 ABSTRACT 3 785 ]4g A gas generatorfor inflating a bag comprising a deflagration composition yielding a gascomprising princi- 52 us. Cl. 23/281; 60/205; 102/39; p y dioxide andwater vapor Comprises a 149/t5; 149/7 49/77; 149 33; 252 1 33 stantiallyhomogeneous mixture of citric acid powder 230/50 AB in the range of fromabout 23 to 37 percent by weight 51 Int. Cl. B01 j 7/00; C06d 5/00 andan oxidizer Powder Selected from lhfi group 53 n w f Search H 23 2 2 2;230 150 sisting of potassium chlorate, potassium perchlorate 60/205 219;102 39; 149/15 7 77 33; sodium chlorate, and sodium perchlorate. Thiscom- 252/188 3 R position is used adjacent a coolant powder comprisingup to about 40 percent by weight of potassium chlo- 5 References Cigedrate and an endothermic decomposition coolant hav- UNITED STATES PATENTSing a thermal decomposition product selected from the class consistingof carbon dioxide and water. 3.3053) 2/1967 Kowallck et al. 23/2813515518 6/1970 Halstcad et al. 23/281 4 Claims, 1 Drawing Figurelllllllll GAS GENERATING COMPOSITIONS AND APPARATUS CROSS REFERENCE TORELATED APPLICATIONS This is a division of application Ser. No. 261,041,filed June 8, l972, now U.S. Pat. No. 3,785,149.

BACKGROUND This application is an improvement on developments describedand claimed in copending U.S. Pat. Application Ser. No. 167,943,entitled Gas Generator Composition and Method," by Hubert G. Timmermanand Vincent Catanzarite. The teachings of this patent application arehereby incorporated by reference.

Governmental requirements for automobile passenger restraint systemsinclude an inflatable bag that momentarily and temporarily restrains apassenger during the critical instant of a collision impact. For safeand successful use the bag must be inflated in a very short time, andthereafter deflated to release the passenger. The gas used to inflatethe bag must be cool enough to avoid damage to the bag and injury to thepassenger. For similar reasons, it is important that hot particles donot reach the interior of the bag. The gases used must have a lowtoxicity, and for this reason, carbon monoxide, nitrogen oxides, sulphurcompounds, and the like are undesirable. It is therefore desirable toprovide compositions that burn to produce a large volume of relativelycool non-toxic gas in a very short time interval for inflating a gasbag.

The composition must be sufficiently stable to sustain the temperature,vibration, and other environmental characteristics of an automobile fora prolonged period. A specified screening test requires, for example,that the composition be maintained at 250F for 100 hours without anydegradation of performance. Such severe requirements effectivelyeliminate from consideration many otherwise apparently suitablematerials.

BRIEF SUMMARY OF THE INVENTION Thus, in practice of this inventionaccording to a presently preferred embodiment, there is provided anon-toxic gas generating composition comprising an organic acid powderselected from the group consisting of citric acid in the range of fromabout 25 to 37 percent by weight, tartaric acid in the range of fromabout to 42 percent by weight, tartronic acid in the range of from aboutto 49.5 percent by weight, and malonic acid in the range of from about20 to 36.7 percent by weight; and a balance of an oxidizer powderselected from the group consisting of potassium chlorate, potassiumperchlorate, sodium chlorate, and sodium perchlorate.

DRAWING These and other features and advantages of the present inventionwill be appreciated as the same becomes better understood by referenceto the following detailed description of presently preferred embodimentswhen considered in connection with the accompanying drawing, whichcomprises a cross section of a gas generator cartridge employing acomposition embodying principles of this invention.

DESCRIPTION The drawing illustrates in longitudinal cross section atypical gas generator cartridge charged with a composition embodyingprinciples of this invention. As illustrated in this presently preferredembodiment, a steel housing 10 forms a gas generator cartridge which canbe threaded into a housing (not shown) or other suitable arrangement forconveying generated gases to an inflatable bag. The gas generatorcartridge is open at its threaded end to permit generated gases toescape freely therefrom. If desired, a frangible or fusible protectivediaphragm may be provided over the open end of the cartridge. At itsclosed end, the cartridge is provided with a conventional bridge wireinitiator 11 and is threaded into a central opening. The initiator 11 isa conventional item wherein a bridge wire" (not shown) is heated by anelectric current when it is de sired to initiate the gas generatingreaction.

Packed into the housing 10in a layer adjacent the ini tiator I1 is abody of propellant 12 described in greater detail hereinafter. In atypical embodiment, the layer 12 may comprise about 10 grams ofpropellant. Adjacent the first propellant layer 12 is an 18 gram layerof coolant 13, described in greater detail hereinafter. After thecoolant layer 13, another propellant layer 14, containing five grams ofpropellant like that in the first layer 12, is packed on top. Finally,an eight gram layer 15 of coolant is provided over the propellant layer14. The coolant 15 is preferably substantially the same as the firstcoolant layer 13. The propellant and coolant layers are preferablypowders pressed in place at a pressure of less than about 5,000 psi.

The two propellant layers 12 and 14 are formed of a mixture of organicacid fuel powder and an oxidizer powder. The organic acid is in the formof a powder having a maximum average particle size less than about l5microns. TI-Ie oxidizer powder preferably has an average particle sizeless than about 25 microns and is selected from the class consisting ofpotassium chlorate, potassium perchlorate, sodium chlorate, and sodiumperchlorate. If the particle size of the organic acid is too large, theeffective surface area for reaction is reduced, and the rate of reactionmay not be sufficient for producing gases fast enough for inflation ofan air bag in an automobile passenger restraint system. The particlesize of the oxidizer powder is preferably less than about 25 microns sothat the reaction rate with the fuel is rapid, and the reaction iscomplete. If the particle size of the oxidizer is greater than about 25microns, unreacted particles may be ejected with the gaseous reactionproducts.

It is particularly preferred that the oxidizer have an average particlesize less than about 15 microns, and the organic acid have an averageparticle size less than about five microns in order to obtain a veryrapid reaction therebetween. Preferably, the particle size of theoxidizer and organic acid are about the same, that is, they do notdiffer from each other more than about percent so that thorough andintimate mixture of the particles is obtained without substantialsegregation. Segregation of the organic acid and the oxidizer powder maylead to erratic burning or yield an incomplete reaction.

The preferred composition of propellant comprises about 32 percent byweight of citric acid and 68 percent by weight of potassium chlorate.The stoichiometric reaction between citric acid and potassium hlorate isC HgO' 3KClO 6CO 4H O 3KCI and the stoichiometric proportion is 34percent by weight of citric acid to 66 percent by weight of potassiumchlorate. Thus, it will be seen that the preferred composition is 2percent by weight rich in oxidizer as compared to the stoichiometricproportion. This composition has proved eminently successful in reducingthe carbon monoxide level in the resultant gases to a very low value.This composition is preferred since it provides an optimum combinationof low toxicity, cool gases, high reliability, rapid and reproducibleburning rate, long term stability at 250F without degradation ofperformance, and low cost. The problem of rapidly, reliably, and safelyinflating an automobile passenger restraint bag is severe, and limitedvariation in the preferred composition has been found. The requirementthat the materials be aged together at 250F for 100 hours is severe andeffectively eliminates most candidate materials. The required low carbonmonoxide level and the requirement that gas temperatures into the bag beless than about l35F further reduce possible candidate compositions.

Citric acid is advantageous since it produces a substantial volume ofgas with a relatively low heat of combustion. Thus, for example, toproduce equal molar quantities of gas, combustion of citric acidproduces only 3l percent as much heat as combustion ofsucrose. For thisreason, the temperature of gas reaching the passenger restraint bag canbe lowerv Some variation in the quantity of citric acid is acceptable incompositions suitable for inflating an automobile passenger restraintbag. Thus, the citric acid concentration can be as low as about 25percent by weight and still produce a commercially acceptableembodiment. Preferably, the citric acid proportion does not drop belowabout 25 percent by weight since lower proportions have an undesirablylow total gas output. The principal proportion of gas produced byreaction of the citric acid and oxidizer derives from the citric acid,and undue reductions in its proportion requires an increased totalquantity of propellant to provide sufficient gas for an automobilepassenger restraint system.

Similarly, the citric acid proportion may be increased up to about 37percent by weight in a commercially acceptable embodiment. If the citricacid is increased above about 37 percent by weight, the carbon monoxidelevel in the resultant gases increases unacceptably.

A few other organic acid powders may be used in practice of thisinvention including tartaric acid, tar tronic acid and malonic acid.Tartaric acid which has the formula C H O reacts stoichiometricly withone and two-thirds mole of potassium chlorate to produce carbon dioxide,water vapor and potassium chloride. The stoichiometric proportion is 42percent by weight of tartaric acid and 58 percent by weight of theoxidizer. The proportion may be decreased to about percent by weight oforganic acid and 80 percent oxidizer powder with acceptable performancein a gas generator for inflation of an automotive passenger restraintbag. Preferably, such a mixture is about 5 percent below stoichiometryfor the organic acid and correspondingly rich in the oxidizer forsuppressing carbon monoxide formation.

Tartronic acid reacts stoichiometricly with one mole of potassiumchlorate to produce carbon dioxide, water vapor and potassium chloride.The stoichiometric proportion is about 49.5 percent organic acid and50.5 percent oxidizer. The proportion of tartronic acid may be reducedto about percent by weight with the oxidizer being present at aboutpercent by weight. Pref erably, the composition is about 5 percent richin oxidizer and correspondingly deficient in fuel for production of anexcess of oxygen and suppression of carbon monoxide formation.

The stoichiometric reaction between malonic acid and potassium chloraterequires one and one-third moles of potassium chlorate for production ofcarbon dioxide and water vapor. This corresponds to about 36.7 percentby weight of the malonic acid and 63.3 percent by weight of theoxidizer. This proportion may be varied to about 20 percent by weight ofmalonic acid and percent by weight of oxidizer powder. Preferably, thecomposition is about 5 percent above stoichiometry in the oxidizer andabout 5 percent deficient below stoichiometry for the organic acid.

It is particularly preferred to employ potassium chlorate as theoxidizing powder since the products of reaction include potassiumchloride at a sufficiently high temperature that it is molten orpossibly in vapor form. Such potassium chloride principally deposits incooler portions of a gas generator system and while so doing, entrapsparticles which might otherwise reach the inflatable bag. Althoughpotassium chlorate is more sensitive than potassium perchlorate inpropellant compositions, no significant safety hazards associated withits use have been identified. If such sensitivity is a problem in someapplications, potassium perchlorate may be used as the oxidizer powderwithin principles of this invention. Potassium perchlorate is not aseffective as potassium chlorate in removing hot particles from the gasstream since its melting point is about 250C higher than the potassiumchlorate. When potassium chlorate is used, it appears that a glassylayer forms on cooler surfaces (not shown) in the fluid passages leadingfrom the gas generator cartridge to the inflatable bag. This glassycoating effectively traps particles from the gas generator cartridge andprevents them from reaching the inflatable bag. The sodium salts may beused but appear less capable of removing hot particles than thepotassium salts.

Although the composition of the propellant has been stated as fuel andoxidizer, it should be understood that some dilution with endothermicdecomposition coolant or the like can be employed. The presentrequirement for passenger restraint systems has a maximum carbonmonoxide level of 750 ppm in the inflating gas. It has been found thatup to about 5 percent by weight dilution of the propellant with zinccarbonate remains within that limit, If a higher level of carbonmonoxide is acceptable, somewhat greater dilution can be used, forexample, as high as about 25 percent. It is, therefore, to be understoodthat the proportions of fuel and oxidizer stated in the compositions arerelative to each other and up to about 5 percent of other materials maybe present in the mixture.

The coolant layers 13 and 15 are preferably a mixture in the range offrom about 20 to 60 percent by weight of potassium chlorate and about 40to 80 percent by weight of zinc carbonate, both of which materialsendothermically decompose when the propellant is ignited, therebyproducing a substantial volume of oxygen and carbon dioxide and coolingthe gases from the propellant. The presence of potassium chlorate in thecoolant produces substantial quantities of potassium chloride which, asmentioned hereinabove, forms a glassy deposit on the cooler walls,thereby trapping particles of zinc oxide and the like ejected from thecoolant. The resultant high concentration of oxygen in the gas from thegas generator is a bonus that helps reduce toxicity and assure completereaction of the organic acid. Some variation in the proportion ofpotassium chlorate in the coolant can be employed in practice of thisinvention. Thus, for example, if desired the potassium chlorate can beas high as about 90 percent by weight without substantially changingeffectiveness of the gas generation. Similarly, potassium chlorate canbe reduced to zero if desired; however, the beneficial oxygen isconcomitantly decreased and the entrapment of zinc oxide powderspartially sacrificed.

If desired, potassium perchlorate can be substituted for potassiumchlorate in the coolant with some decrease in the formation of a glassydeposit within the gas generator, and hence less efficacious sweeping ofhot particles from the gases. Similarly sodium chlorate and sodiumperchlorate may be used.

Substitution for zinc carbonate can also be provided in the coolant,although this is a preferred material. Other suitable materials may beselected from the group consisting of magnesium carbonate, manganesecarbonate, barium carbonate, calcium carbonate, potassium bicarbonate,hydrated magnesium carbonate, hydrated zirconium oxide, borax, andbarium oxide octahydrate. If it is acceptable to have a caustichydroxide as a possible reaction product, sodium carbonate and sodiumbicarbonate are suitable coolants. The sodium oxides remaining fromdecomposition of sodium carbonate and sodium bicarbonate may combinewith potassium chloride to form a slag that remains in the gas generatorand causes no harm in the gas bag.

A variety of compositions have been tested for suitability for practiceof this invention. Some of these tests have been in the nature ofscreening tests where the composition was burned and the reactionobserved without utilizing the gases generated. Rate and completeness ofreaction are observed in unconfined burning. Experience shows thatcompositions burning in the same manner as successful compositions inthe unconfined screening tests will perform satisfactorily in baginflation tests. Other compositions were placed in a confined gasgenerator and the gases used for inflating a fabric bag. The followingcompositions were tested: 1. tartaric acid, 80% potassium chlorate 2.30% tartaric acid, 70% potassium chlorate 3. 38% tartaric acid, 62%potassium chlorate 4. 42% tartaric acid, 58% potassium chlorate 5. 46.5%tartaric acid, 53.5% potassium perchlorate 6. 45% tartaric acid, 55%potassium perchlorate 7. 26.6% tartaric acid, 55.4% potassium chlorate,18%

zinc carbonate 8. 22.8% tartaric acid, 53.2% potassium chlorate, 24%

zinc carbonate 9. 49.5% tartronic acid, 50.5% potassium chlorate 10.36.7% malonic acid, 63.3% potassium chlorate l 1. 34.3% citric acid,66.7% potassium chlorate 12. 32% citric acid, 68% potassium chlorate 13.25% citric acid, potassium chlorate What is claimed is:

l. A gas generator for inflating a bag comprising:

a pressure resistant vessel having a closed end and an open end;

a body of compacted powders in the vessel, said body comprising a firstportion consisting essentially of an intimate mixture of citric acid inthe range of from about 25 to 37 percent by weight and the balanceselected from the group consisting of potassium chlorate, potassiumperchlorate, sodium chlorate, and sodium perchlorate, and

a second portion immediately adjacent to the first portion comprising anintimate mixture of up to about 60 percent by weight of potassiumchlorate and the balance selected from the group consisting of magnesiumcarbonate, manganese carbonate, zinc carbonate, barium carbonate,calcium carbonate, potassium bicarbonate, hydrated magnesium carbonate,hydrated zirconium oxide, borax, and barium oxide octahydrate; and

means at the closed end of the vessel for raising a portion of thecompacted powders to its autoignition temperature.

2. A gas generator as defined in claim 1 wherein the potassium chloratein the second portion is present as about 40 percent by weight and thebalance is zinc carbonate.

3. A gas generator as defined in claim 1 wherein the citric acid ispresent as about 32% by weight and the balance is potassium chlorate.

4. A gas generator as defined in claim 1 wherein the body of compactedpowders comprises a plurality of alternating layers of the first portionand the second portion.

1. A GAS GENERATOR FOR INFLATING A BAG COMPRISING: A PRESSURE RESISTANTVESSEL HAVING A CLOSED END AND AN OPEN END; A BODY OF COMPACTED POWDERSIN THE VESSEL, SAID BODY COMPRISING A FIRST PORTION CONSISTINGESSENTIALLY OF AN INTIMATE MIXTURE OF CITRIC ACID IN THE RANGE OF FROMABOUT 25 TO 37 PERCENT BY WEIGHT AND THE BALANCE SELECTED FROM THE GROUPCONSISTING OF POTASSIUM CHLORATE, POTASSIUM PERCHLORATE, SODIUMCHLORATE, AND SODIUM PERCHLORATE, AND A SECOND PORTION IMMEDIATELYADJACENT TO THE FIRST PORTION COMPRISING AN INTIMATE MIXTURE OF UP TOABOUT 60 PERCENT
 2. A gas generator as defined in claim 1 wherein thepotassium chlorate in the second portion is present as about 40 percentby weight and the balance is Zinc carbonate.
 3. A gas generator asdefined in claim 1 wherein the citric acid is present as about 32% byweight and the balance is potassium chlorate.
 4. A gas generator asdefined in claim 1 wherein the body of compacted powders comprises aplurality of alternating layers of the first portion and the secondportion.